The present invention relates to a method for manufacturing a semiconductor device. More specifically, the invention relates to a method for manufacturing a semiconductor device provided with protrudent electrodes used as an external wiring to make electrical connection with a conductive pattern formed on a circuit substrate.
Recently, with advancement of smaller and higher-performance semiconductor devices, a semiconductor chip has been miniaturized and the number of terminals (connection terminals) has been increasing. In connection with this, pitches of the connection terminals are being made finer. A result of this is wide spreading use of packaging methods by which a semiconductor device is packaged in a tape carrier package (hereinbelow referred to as a TCP) by inner lead bonding (hereinbelow referred to as ILB) and packaged on a circuit substrate by direct flip-chip bonding with its face down. Further, like the ILB and the flip-chip bonding, the packaging methods by which fine pitch terminals can be connected at once regardless of the number of connection terminals are adopted by various semiconductors.
In order to realize these packaging methods, it is required to form a protrudent electrode (hereinbelow referred to as a bump) for connection on an electrode pad of a semiconductor chip.
Processes of manufacturing a bump in practical applications include a non-electrolytic bump process by which an Au (gold) bump or a solder bump is formed by electrolytic plating which utilizes electrocoating by electrolysis, and a wire bump process which utilizes wire bonding by metal fine lines.
The electrolytic plating bump process is advantageous because it provides high throughput by wafer batch processing, a large number of terminals, and finer pitch. However, the electrolytic plating bump process requires forming a barrier metal layer which is also used as a conductive film for electrolytic plating and forming a window in a bump forming portion by coating, exposuring, and developing a photoresist. Further, in the electrolytic plating bump process, since it is necessary to employ a step of forming the metal layer for electrolytic plating and a masking step using a photoresist for forming a bump selectively, the step of forming the bump is complicated. Further, in the electrolytic plating bump process, it is required to use such equipment as sputtering equipment and photo equipment other than electrolytic plating equipment. Thus, there is a problem that equipment investment becomes very large.
On the other hand, in the wire bump process, bumps are formed successively on respective electrode pads with wire bonder. Thus, in the wire bump process, throughput is low and it is difficult to increase the number of terminals. Further, in realizing finer pitch, while the limit of the pitch of the electrode pad in the electrolytic plating bump process is about bump width+5 xcexcm (for example, when the bump width is 20 xcexcm, the pitch width is 25 xcexcm), the finest pitch of the electrode pad in the wire bump process is about 75 xcexcm. Note that, since it is possible to form the bump only with the wire bonder in the wire bump process, there is an advantage that equipment investment can be suppressed.
As described above, semiconductor devices having a bump have been manufactured conventionally by making use of characteristics of the respective methods for forming a bump. However, recently, an non-electrolytic plating bump process is being developed as a new method for forming a bump.
The non-electrolytic plating bump process is to perform non-electrolytic plating selectively on an electrode pad made of or mainly made of Al (aluminum) which is formed on the semiconductor substrate in a semiconductor device. Further, in the non-electrolytic plating bump process, unlike the electrolytic bump process, it is not required to form a conductive film for plating by the sputter equipment or form a window using a photoresist in a bump forming portion by photo equipment. Thus, the process can be simplified and less equipment investment is required. Further, the non-electrolytic plating bump process can realize lower cost while having the advantageous characteristics of higher throughput by wafer batch processing, and finer pitches, which are common characteristics of plating bump processes.
Here, as the non-electrolytic plating bump process in the case where Ni (nickel) is used as the main component of the bump, Ni/Au plating bump process is described below with reference to FIG. 5(a) to FIG. 5(e).
First, as shown in FIG. 5(a), an electrode pad 2 made of or mainly made of Al is formed on a semiconductor substrate 1. Further, a protecting film 3 (insulating protecting film) having an insulating property is stacked on the electrode pad 2 so as to cover the electrode pad 2. Next, a portion of an upper surface of the electrode pad 2 is exposed, for example, by etching a portion of the protecting film 3 on the electrode pad 2. Thus, the protecting film 3 having an opening 3a on the electrode pad 2 is patterned.
Next, as shown in FIG. 5(b), an oxide film 4 on the surface of the electrode pad 2 in the opening 3a of the protecting film 3 and a residual thin film (not shown) of the protecting film 3 are removed. Thereafter, a zincate process is performed by a substitution reaction of Al and Zn (zinc), and as shown in FIG. 5(c), Al on the surface of the electrode pad 2 is substituted with Zn. Thus, a Zn layer 5 is formed on the surface of the electrode pad 2.
Next, the semiconductor substrate 1 processed by the zincate process is immersed in a non-electrolytic plating solution to carry out the non-electrolytic plating process. For example, the semiconductor substrate 1 on which the Zn layer 5 is formed is immersed in a non-electrolytic Ni plating solution, so as to carry out the non-electrolytic Ni plating process by a non-electrolytic Ni plating reaction. In the non-electrolytic Ni plating reaction, first, Zn of the Zn layer 5 and Ni undergo a substitution reaction and Ni is deposited, thereby substituting Zn with Ni. Thereafter, as shown in FIG. 5(d), Ni is deposited progressively by the self catalytic reaction in which the substituted Ni itself acts as a catalyst, thus forming an Ni bump 6.
In the case where the bump is made of a material which forms an oxide film on its surface like the Ni bump 6, an Au thin film is formed on the surface of the bump so as to prevent oxidation on the surface of the resulting bump.
In this case, after non-electrolytic Ni plating is finished, for example, displacing Au plating is performed so as to prevent oxidation on an Ni surface of the Ni bump 6. Thus, as shown in FIG. 5(e), Au is deposited on the Ni surface, and an Au layer 9 is formed on the Ni bump 6. This completes the non-electrolytic Ni/Au plating bump process.
As described above, in forming the non-electrolytic Ni plating bump, it is not required to form a conductive film for plating by sputter equipment, or form a window in a bump forming portion using a photoresist by photo equipment. Thus, forming the non-electrolytic Ni plating bump has an advantage that less equipment investment is required. Further, since inexpensive Ni is used as a main material and throughput is good, forming the non-electrolytic Ni plating bump costs less than forming the Au bump by the electrolytic plating bump process.
However, as a result of study by the inventor of the present invention, it was found that the bump formed by the non-electrolytic plating bump process poses a problem in a pressure cooker test (hereinbelow referred to as PCT), which is an index of guaranteed quality.
In the non-electrolytic plating bump process, the non-electrolytic plating process is performed selectively only on the electrode pad 2 in the opening 3a of the protecting film 3. Here, the reaction of the non-electrolytic Ni plating proceeds as the Zn (or Pd) of the Zn layer 5 which is formed by substitution with Al is substituted with Ni on the electrode pad 2 exposed in the opening 3a of the protecting film 3 made of the oxide film etc. Thereafter, the reaction proceeds by the self catalytic reaction in which Ni itself becomes a catalyst to deposit Ni. Thus, Ni deposited by non-electrolytic Ni plating does not form any chemical bond except with the Ni which was substituted in advance or deposited already, and Ni is deposited only on Ni. Therefore, as shown in FIG. 5(d) and FIG. 5(e) and FIG. 6, since Ni has no bond with the protecting film 3, there exists a narrow gap 7 between the Ni bump 6 and the protecting film 3 facing the Ni bump 6.
Thus, as shown in FIG. 5(d) and FIG.5(e) and FIG. 6, non-electrolytic Ni plating solution remains as plating solution residue 8 (component of the non-electrolytic Ni plating solution) in the narrow gap 7. As a result, the Ni bump 6 is formed with the plating solution residue 8 remaining in the narrow gap 7.
A semiconductor device manufactured with the plating solution residue 8 remaining in the narrow gap 7, for example, was packaged in a TCP and was examined by PCT (121xc2x0 C., 2.026xc3x97105 Pa) which is an item of reliability evaluation. The result shows that the remaining plating solution residue 8 melted and leaked from the narrow gap 7 in about 100 hours, and a leaking defect between adjacent terminals occurred. Thus, the plating solution residue 8 causes unreliability of the semiconductor device.
The plating solution residue 8 remaining in the narrow gap 7 cannot be removed easily and completely by normal pure water cleaning.
Japanese Unexamined Patent Publication No. 326848/1995 (Tokukaihei 7-326848)(published date: Dec. 12, 1995) discloses the following technique as a technique for cleaning a plated substrate concerning a method for manufacturing a gold plating mold substrate used as a chip on board substrate (hereinbelow referred to as COB). When a circuit (a wiring pattern) is formed by underlayer plating and gold plating on the COB substrate which is provided with pits for installing components, a brightener which is included in the plating solution for the underlayer plating is absorbed in a plating film formed by the gold plating. In this case, a plating surface for wire bonding is stained, and a wire bonding ability on the plating surface suffers. In the foregoing publication, the plating surface for wire bonding is cleaned by an aqueous solution including hydrogen peroxide and ammonia so as to prevent the wire bonding ability from degrading.
As described above, in a semiconductor device for flip chip packaging and ILB, it is required to form a bump on an electrode pad by non-electrolytic plating. In forming a bump, a narrow gap is created between the bump (Ni plate) and a protecting film, and plating solution residue exists in the gap. However, the foregoing Japanese Unexamined Patent Publication No. 326848/1995 does not disclose removing plating solution residue remaining in the narrow gap or a method for this.
Further, in the electrolytic plating bump process, after a conductive film for electrolytic plating is formed on a wafer, a window is formed using a photoresist to form a bump selectively. After the bump is formed, the photoresist is removed. Therefore, the plating solution residue remaining between the photoresit and the bump is removed completely in a process of removing the photoresist. Thus, a narrow gap exists between a bump and a protecting film, and a component of a plating solution remains as residue in the narrow gap. This is a problem intrinsic to the structure of the non-electrolytic plating bump process.
It is an object of the present invention, from the viewpoint of the foregoing problems, to provide a method for manufacturing a highly reliable semiconductor device which can be provided at low cost while realizing high throughput, finer pitch, and improved moisture resistance. More specifically, according to the object of the present invention, when forming a protrudent electrode of the semiconductor by non-electrolytic plating by which a high throughput and finer pitch can be realized and the protrudent electrode can be formed at low cost, the present invention is to remove plating solution residue in a narrow gap between the protrudent electrode and a protecting film, which is intrinsic to the non-electrolytic plating used to form the protrudent electrode, so that moisture resistance of the semiconductor device can be improved. As a result, reliability of the semiconductor device can be improved.
A manufacturing method of a semiconductor device according to the present invention, to achieve the foregoing object, includes two steps. A first step is a step of forming a protrudent electrode (for example, a nickel bump) by non-electrolytic plating in an opening of an insulating protecting film formed on an electrode pad provided on a semiconductor substrate. A second step is a step of removing plating solution residue in a gap between the protrudent electrode and the insulating protecting film.
The protrudent electrode is formed selectively by non-electrolytic plating on the electrode pad formed on the semiconductor substrate. Further, unlike the case where the protrudent electrode is formed by electrolytic plating, it is not required to form a conductive film for plating by sputter equipment or a window in a bump forming portion using a photoresist. Therefore, by forming the protrudent electrode by non-electrolytic plating, steps can be simplified and equipment investment can be reduced. Therefore, forming the protrudent electrode by non-electrolytic plating can reduce cost while having advantageous characteristics such as high throughput and finer pitch.
On the other hand, the protrudent electrode formed by non-electrolytic plating is formed selectively on the electrode pad in the opening of the insulating protecting film, so that there is no chemical bond between the resulting protrudent electrode and the insulating protecting film. For example, in the case where the protrudent electrode is formed by non-electrolytic nickel plating in the opening, the protrudent electrode is formed as nickel is deposited on nickel by the self catalytic reaction. Thus, a narrow gap exists between the protrudent electrode and the insulating protecting film facing the protrudent electrode. Further, a plating solution is trapped in the narrow gap in the process of forming the protrudent electrode as the plating layer grows by the non-electrolytic plating. In the case where a semiconductor device manufactured with the plating solution residue remaining in the narrow gap is examined by PCT (121xc2x0 C., 2.026xc3x97105 Pa), the remaining plating solution residue melts and leaks from the narrow gap, and a leaking defect between terminals is caused.
Thus, it is very effective to form the protrudent electrode by non-electrolytic plating and remove trouble-making plating solution residue in the narrow gap between the protrudent electrode and the insulating protecting film which occurs in forming the protrudent electrode by non-electrolytic plating. That is, compared with the case where the protrudent electrode is formed by electrolytic plating, steps can be simplified and equipment investment can be reduced. Thus, the foregoing measure can reduce cost while having advantageous characteristics such as high throughout and finer pitch. Further, the foregoing measure can prevent defects such as a leak between terminals, so that moisture resistance of the semiconductor device can be improved. As a result, reliability of the semiconductor device can be improved.